CA and federal copyright infringement law, can an altered image be used on a t-shirt without infringing copyright

There is no set percentage. You are allowed to use someone else's copyrighted work only in limited circumstances - in a critique or a parody are two such examples. Remember that the person used in the photograph has a right to privacy and a right to publicity and that the person who took the photograph or designed the image also may have an interest in the work as well. Each of the programs you list also has a EULA that limits the commercial use of the images in their program.

Dear Sir or Madam,

It sounds like you would like to use someone else's image, or a derivative of someone else's image, on clothing. An easy solution would be to purchase a license from the copyright owner. With the proper type of license agreement with the copyright owner, you will be able to legally use the image, and images that you create from the original image. Most importantly, you will be able to sell the shirts legally.

An attorney can draft a license agreement for you for a minimal fee.

Best of luck.

-Tomas M. Flores, Esq.

The two previous answers are accurate. As in many areas of law, especially intellectual property, there is no set equation or checklist for determining infringing activity. Copyright law basically evaluates the original work and the allegedly infringing work and asks if there is a substantial similarity between the two. There are numerous court decisions that have gone in a hundred different ways on this topic with a hundred different elements.